1. Field of the Invention
The present invention relates generally to medical apparatus and methods. More particularly, the present invention relates to a method and system for accessing a biopsy site in solid tissue while protecting the access tract from seeding with tumor cells.
Percutaneous or “needle” biopsy of suspected malignancies is now in common use. Typically, an access sheath, such as a needle or cannula, is introduced through solid tissue to provide access to a target site in the tissue. A biopsy needle, biopsy gun, or similar device is then introduced through the needle or cannula to obtain a small tissue sample. The biopsy device is withdrawn through the needle or cannula, and the needle or cannula then withdrawn through the tissue tract to complete the procedure. The needle or cannula may also be incorporated as an integral portion of the biopsy device.
While quite useful and generally successful, such “needle biopsy” procedures raise concern over possible “seeding” of tumor cells along the tissue tract by the needle or cannula as it is withdrawn. Seeding refers to the unintentional transport of cells from the biopsy site into the tissue tract. Such seeding can inadvertently spread the tumor beyond its original location, making treatment of the tumor more difficult.
The use of a separate needle or cannula is advantageous since it allows multiple biopsy samples to be taken from the same location without the need to form a separate puncture for each sample. Integral systems where the needle or cannula is part of the biopsy device require separate punctures to be formed, but it can be manufactured with smaller diameters than biopsy systems including separate access sheaths and biopsy components. Biopsy systems including separate access sheaths are further advantageous in that the access sheath isolates the tissue tract from the biopsy-capturing component of the system. The relatively large size of the access sheath, however, can itself dislodge tumor cells and potentially seed the tissue tract when the access sheath is removed.
In order to minimize the risk of tumor cell seeding in biopsy tissue tracts, placement of a sheath over the biopsy instrument has been proposed by Woitzik and Krauss, Surgical Endoscopy (2003) 17:311-314. A polyethylene sheath is positioned so that it covers the exterior and interior of an access cannula, i.e., by folding the sheath over the leading (distal) end of the cannula. The cannula is introduced to a target site using a stylet in a generally conventional manner. After taking a sample through the lumen of the cannula with a separate biopsy instrument, the biopsy instrument is removed, and the inside of the sleeve (i.e. that portion which passes through the lumen of the cannula) is pulled back through the cannula lumen to remove the cannula. In this way, the sheath on the exterior of the cannula is inverted or invaginated into the lumen of the cannula as the sheath is withdrawn. Any tumor cells which might adhere to the exterior of the cannula after the biopsy has been completed will be drawn into the lumen of the cannula, thus reducing the risk of tumor cell seeding.
While the cannula and method of Woitzik and Krauss will theoretically limit the risk of tumor cell seeding of tissue tracts, the particular approach suffers from certain disadvantages. The sheath which is present in the lumen of the cannula can be damaged by passage of the stylet and/or the biopsy instrument through the cannula. Should the sheath be damaged, it is possible that the sheath will break as it is being pulled, thus preventing complete invagination of the sheath as the cannula is withdrawn. Moreover, folding of the sheath over the distal end of the cannula requires that the cannula tip be blunt. Such a blunt tip prevents designs having sharpened or other self-introducing designs. Additionally, in order for the exposed sheath portion of Woitzik and Krauss to be isolated within the device, the cannula sheath cannot be allowed to simultaneously move proximally in the tissue tract. Such simultaneous movement would allow exposed sheath portions to contact and potentially seed the tissue tract in a manner analogous to unsheathed access cannula. For that reason, the Woitzik and Krauss cannula must be pushed forwardly (i.e., in a direction into the body) while being pulled out of the body by the inverting sheath. Thus, the apparatus must be pushed and pulled at the same time, which is not always an easy step to perform. Moreover, the forward pressure of the cannula exerts significant friction against the sheath as it is everted. This is both difficult and significantly increases the risk of tearing the sheath as the cannula is being withdrawn.
For these reasons, it would be desirable to provide additional and improved tissue biopsy systems which reduce the risk of tumor cell seeding of percutaneous tissue access tracts. It would be further desirable to provide systems and methods employing access cannulas where the cannula is covered with a protective sleeve which is not located within a lumen of the cannula and which does not need to be folded over a leading or distal tip of the cannula. It would further be desirable to provide cannulas having protective sleeves where withdrawal of the cannula removes the sleeve in a manner which reduces the risk of tumor cell seeding and which pulls only the trailing edge of the sleeve as the cannula is withdrawn. At least some of these objectives will be met by the inventions described hereinbelow.
2. Description of the Background Art
The use of sleeves for protecting biopsy needles and cannulas is described in U.S. Pat. Nos. 4,262,677; 5,037,379; DE 10031661A1; and Woitzik and Krauss (2003) Surg. Endosc. 17:311-314. Biopsy needles are described in U.S. Pat. Nos. 4,958,625; 5,090,419; and 5,368,045. Other biopsy devices having collection bags are described in U.S. Pat. Nos. 6,344,026 and 6,022,362. The use of an everting sleeve composed of thin, tensilized polytetrafluoroethylene for introducing catheters to body lumens is described in U.S. Pat. Nos. 5,531,717; 5,676,688; 5,711,841; 5,897,535; 6,007,488; 6,240,968; and EP605427B1. The use of braided and other radially expanding sleeves for introducing sheaths, surgical tools, and other articles is described in U.S. Pat. Nos. 5,431,676; 5,454,790; 5,814,058; 5,836,913; 6,080,174; 6,325,812; and 6,494,893. A biopsy device with a removable sheath is commercially available from Boston Scientific, under the tradename “ASAP Detachable Biopsy System.”